1. Field
This invention relates generally to spacecraft components such as mirrors, optical sensors, solar cells and the like having critical surfaces whose contamination would shorten the useful life of the components and thereby also the spacecraft mission life. The invention relates more particularly to a method of protecting such spacecraft components against critical surface contamination until the spacecraft arrives in outer space, and then automatically exposing the protected surfaces in their pristine state to the space environment. The invention relates also to protected spacecraft components of the class described.
2. Prior Art
As a result of the ever increasing complexity and cost of spacecraft, extending spacecraft mission life has become a primary concern. Extending mission life, in turn, requires extending the useful life of all the spacecraft components. This invention is concerned with contributing to extended spacecraft mission life by extending the useful life of spacecraft components having critical surfaces whose contamination would shorten the useful life of the components. Examples of such components are optical sensors, mirrors including both first and second surface mirrors, solar cells, and the like.
Optimum performance of spacecraft components of the class described is dependent upon their arrival in outer space with their critical surfaces in a pristine state and retention of these surfaces in at least a highly efficient state approaching their pristine state over the entire anticipated spacecraft mission life. Optical sensors, mirrors, solar cells, and the like, for example, all have optical surfaces which must retain a high level of transmissibility and reflectivity for longer and longer periods of time.
During fabrication of the components, their critical surfaces are prepared or conditioned to the required pristine state. Unless properly protected afterwards, however, the critical surfaces can be seriously degraded by atmospheric and other contaminants, both liquid and solid. Optical surfaces are particularly prone to degredation of their optical properties by such contaminants. Moreover, many substances which may contaminate optical surfaces, such as organic polymeric contaminants, may undergo cross-linking or other physical and/or chemical change which causes them to harden and darken when exposed to the outer space radiation environment. This results in further serious degredation of the optical properties of the surfaces.
It is absolutely essential, therefore, that critical surfaces of spacecraft components be kept free of contamination and maintained in their pristine state throughout any production, fabrication and assembly procedures which may occur after conditioning of the surfaces to the desired pristine state. Thereafter, the surfaces must be protected against contamination and maintained in their pristine state during subsequent integration and launch of the spacecraft and transfer of the spacecraft into final orbit or trajectory.
Elaborate cleaning and protection procedures have been devised for maintaining critical spacecraft surfaces free of contamination. Most of these procedures involve mechanical shielding of the surfaces in some way. These prior surface protection procedures, however, are not totally satisfactory and tend to be relatively complicated, costly and otherwise not totally acceptable for spacecraft use.
As explained in the following description, the present invention utilizes a subliming coating, that is a coating which gasifies directly from the solid state, to protect critical spacecraft surfaces against contamination. Heretofore, subliming materials have been used on space craft to accompolish a variety of useful operative functions. For example:
1. As a time delay, electrical switches. PA1 2. As a temporary mechanical structure. PA1 3. As an encapsulation material for preventing damage during launch to delicate mechanical, electrochemical or optical devices. PA1 4. As a source of impulse for gently controlling the altitude or adjusting the orbit of spacecraft.
U.S. Pat. No. 4,343,964 discloses a subliming material used to cover a tacky substance within an electrical transmission line for ease of handling during fabrication. Sublimation of the material is effected after fabrication to uncover the tacky substance which then catches any particles within the transmission line to prevent shorting. U.S. Pat. Nos. 4,199,620, 4,325,744 and 4,424,079 disclose coatings which are applied to surfaces and then stripped away to remove contaminants, rust and the like, from the surfaces. These latter concepts, while disclosing surface coatings which are removable by sublimination in the case of U.S. Pat. No. 4,343,964, and are removable to strip away surface contaminents in the case of the other mentioned patents, are obviously not applicable to the problem addressed by this invention, i.e., protecting critical spacecraft surfaces until their arrival in outer space.
A definite need exists, therefore, for an improved critical surface protection technique for shielding critical spacecraft surfaces against contamination and thereby maintaining the surfaces in a pristine state until the spacaecraft reaches its final orbit or trajectory in outer space.